Circuit-connecting material and circuit terminal connected structure and connecting method

ABSTRACT

A circuit-connecting material which is interposed between circuit electrodes facing each other and electrically connects the electrodes in the pressing direction by pressing the facing electrodes against each other; the circuit-connecting material comprising as essential components (1) a curing agent capable of generating free radicals upon heating, (2) a hydroxyl-group-containing resin having a molecular weight of 10,000 or more and (3) a radical-polymerizable substance. Also provided are a circuit terminal connected structure and a circuit terminal connecting method which make use of such a material.

This application is a divisional of U.S. patent application Ser. No.11/227,186, filed Sep. 16, 2005, which is a divisional of U.S. patentapplication Ser. No. 10/860,578, filed Jun. 4, 2004, which is adivisional of U.S. patent application Ser. No. 09/402,274 (Now U.S. Pat.No. 6,777,464) filed Dec. 16, 1999, which is a National PhaseApplication of PCT/JP98/01467, filed Mar. 31, 1998, which claimspriority from Japanese Patent Application No. 09-079422, filed Mar. 31,1997, Japanese Patent Application No. 09-079424, filed Mar. 31, 1997,and Japanese Patent Application No. 09-252933, filed Sep. 18, 1997 theentire disclosures of the above patent applications are herebyincorporated by reference.

TECHNICAL FIELD

This invention relates to a circuit-connecting material to be interposedbetween circuit electrodes facing each other and, the facing electrodesbeing pressed against each other, to electrically connect the electrodesin the pressing direction. It also relates to a circuit terminalconnected structure and a circuit terminal connecting method.

BACKGROUND ART

Epoxy resin adhesives are widely used for various purposes of electric,electronic, construction, automobile, aircraft and so forth because theycan attain a high bonding strength and have excellent water resistanceand heat resistance. In particular, one-part epoxy resin adhesives areused in the form of films, pastes or powders because they make itunnecessary to mix the base resin and the curing agent and can be usedwith ease. In this case, it is general to attain specific performancesby using epoxy resins, curing agents and modifiers in variouscombinations (e.g., Japanese Patent Application Laid-open (KOKAI) No.62-141083).

However, film type epoxy resin adhesives as disclosed in the aboveJapanese Patent Application Laid-open (KOKAI) No. 62-141083, thoughhaving an excellent operability, have been required to be heated atabout 140 to 180° C. when connected in a time of about 20 seconds, andat about 180 to 210° C. when connected in 10 seconds.

This is because catalyst type curing agents, which are inert at normaltemperature, are used so that both short-time curability (rapidcurability) and storage stability (storability) can be achieved toattain a better stability, and hence no sufficient reaction can takeplace when cured.

In recent years, in the field of precision electronic equipment,circuits are being made higher in density, resulting in very small widthof electrodes and very narrow spaces between electrodes. Hence, therehas been a problem that the wiring comes off, separates or positionallydeviates under connecting conditions for circuit-connecting materialsmaking use of conventional epoxy resin adhesives. Also, in order toimprove production efficiency, it is increasingly sought to shorten theconnecting time to 10 seconds or less, making it indispensable to attainlow-temperature rapid curability.

DISCLOSURE OF THE INVENTION

The present invention provides an electric and electroniccircuit-connecting material having a superior low-temperature rapidcurability and also having a long pot life.

A first circuit-connecting material of the present invention is acircuit-connecting material which is interposed between circuitelectrodes facing each other and electrically connects the electrodes inthe pressing direction by pressing the facing electrodes against eachother;

the circuit-connecting material comprising as essential components thefollowing components (1) to (3):

-   (1) a curing agent capable of generating free radicals upon heating;-   (2) a hydroxyl-group-containing resin having a molecular weight of    10,000 or more; and-   (3) a radical-polymerizable substance.

As the curing agent capable of generating free radicals upon heating,preferred are curing agents having a 10-hour half-life temperature of40° C. or above and a 1-minute half-life temperature of 180° C. orbelow, and peroxyesters are usable.

The radical-polymerizable substance may contain a radical-polymerizablesubstance represented by the following chemical formula (a).

wherein n is an integer of 1 to 3.

As the hydroxyl-group-containing resin having a molecular weight of10,000 or more, preferred are phenoxy resins, in particular, phenoxyresins modified with a carboxyl-group-containing elastomer and phenoxyresins modified with an epoxy-group-containing elastomer.

A second circuit-connecting material of the present invention is acircuit-connecting material which is interposed between circuitelectrodes facing each other and electrically connects the electrodes inthe pressing direction by pressing the facing electrodes against eachother;

the circuit-connecting material comprising as essential components thefollowing components (3) and (4):

-   (3) a curing agent capable of generating free radicals upon heating    and having a 10-hour half-life temperature of 40° C. or above and a    1-minute half-life temperature of 180° C. or below; and-   (4) a radical-polymerizable substance.

As the curing agent capable of generating free radicals upon heating,peroxyesters are preferred.

The circuit-connecting material described above may contain an acrylicrubber.

A third circuit-connecting material of the present invention is acircuit-connecting material which is interposed between circuitelectrodes facing each other and electrically connects the electrodes inthe pressing direction by pressing the facing electrodes against eachother;

the circuit-connecting material having, in the measurement with adifferential scanning calorimeter (DSC) at 10° C./min., an exothermicreaction arising temperature (Ta) within a range of from 70° C. to 110°C., a peak temperature (Tp) of Ta+5 to 30° C. and an end temperature(Te) of 160° C. or below.

The above circuit-connecting material may contain conductive particles.

The circuit terminal connected structure of the present inventioncomprises a first circuit member having a first connecting terminal anda second circuit member having a second connecting terminal;

the circuit members being disposed in such a way that the firstconnecting terminal and the second connecting terminal face each other;the circuit-connecting material described above being interposed betweenthe first connecting terminal and the second connecting terminal whichface each other; and the first connecting terminal and the secondconnecting terminal which face each other being electrically connected.

The circuit terminal connecting method of the present inventioncomprises;

disposing a first circuit member having a first connecting terminal anda second circuit member having a second connecting terminal, in such away that the first connecting terminal and the second connectingterminal face each other and interposing the circuit-connecting materialdescribed above, between the first connecting terminal and the secondconnecting terminal which face each other, followed by heating andpressing to electrically connect the first connecting terminal and thesecond connecting terminal which face each other.

The circuit terminal connected structure of the present invention mayalso comprise a first circuit member having a first connecting terminaland a second circuit member having a second connecting terminal;

the circuit members being disposed in such a way that the firstconnecting terminal and the second connecting terminal face each other;a circuit-connecting material capable of curing upon radicalpolymerization being interposed between the first connecting terminaland the second connecting terminal which face each other; the surface ofat least one of the first and second connecting terminals being formedof a metal selected from gold, silver, tin and platinum group metals;and the first connecting terminal and the second connecting terminalwhich face each other being electrically connected.

The circuit terminal connecting method of the present invention may alsocomprise;

disposing a first circuit member having a first connecting terminal anda second circuit member having a second connecting terminal, in such away that the first connecting terminal and the second connectingterminal face each other and interposing a circuit-connecting materialcapable of curing upon radical polymerization, between the firstconnecting terminal and the second connecting terminal which face eachother, followed by heating and pressing to electrically connect thefirst connecting terminal and the second connecting terminal which faceeach other;

the surface of at least one of the first and second connecting terminalsbeing formed of a metal selected from gold, silver, tin and platinumgroup metals; and the circuit-connecting material capable of curing uponradical polymerization being formed on one connecting terminal whosesurface is formed of the metal selected from gold, silver, tin andplatinum group metals, and thereafter the other connecting terminalbeing registered, followed by the heating and pressing to connect them.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the step of provisionalconnection of circuit substrates, illustrating an embodiment of thepresent invention.

FIG. 2 is a cross-sectional view showing the step of main connection ofcircuit substrates, illustrating an embodiment of the present invention.

BEST MODE FOR PRACTICING THE INVENTION

The curing agent capable of generating free radicals upon heating, usedin the present invention, may include peroxide compounds and azocompounds which are capable of being decomposed to generate freeradicals upon heating, and may appropriately be selected in accordancewith the intended connecting temperature, connecting time, pot life orthe like. In view of high reactivity and pot life, organic peroxideshaving a 10-hour half-life temperature of 40° C. or above and a 1-minutehalf-life temperature of 180° C. or below are preferred, and organicperoxides having a 10-hour half-life temperature of 60° C. or above anda 1-minute half-life temperature of 170° C. or below are more preferred.

The curing agent may preferably be mixed in an amount of from 0.05 to 10parts by weight, and more preferably from 0.1 to 5 parts by weight,based on 100 parts by weight of the total weight of thehydroxyl-group-containing resin having a molecular weight of 10,000 ormore and radical-polymerizable substance.

The curing agent may be selected from diacyl peroxides,peroxydicarbonates, peroxyesters, peroxyketals, dialkyl peroxides,hydroperoxides and silyl peroxides. In order to keep connectingterminals of the circuit member from corrosion, chloride ions or organicacids contained in the curing agent may preferably be in an amount of5,000 ppm or less. Curing agents that may generate less organic acidsafter heating and decomposition are more preferred.

Stated specifically, the curing agent may preferably be selected fromperoxyesters, dialkyl peroxides, hydroperoxides and silyl peroxide, andmay more preferably be selected from peroxyesters with which highreactivity can be obtained.

These curing agents may be used in an appropriate combination.

As the peroxyesters, usable are cumyl peroxyneodecanoate,1,1,3,3-tetramethylbutyl peroxyneodecanoate, 1-cyclohexyl-1-methyethylperoxynoedecanoate, t-hexyl peroxyneodecanoate, t-butyl peroxypivarate,1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate,2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane,1-cyclohexyl-1-methyethyl peroxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, t-butyl peroxy-2-ethylhexanoate, t-butylperoxyisobutyrate, 1,1-bis(t-butylperoxy)cyclohexane, t-hexylperoxyisopropylmonocarbonate, t-butyl peroxy-3,5,5-trimethylhexanoate,t-butyl peroxylaurate, 2,5-dimethyl-2,5-di(m-toluoylperoxy)hexane,t-butyl peroxyisopropylmonocarbonate, t-butylperoxy-2-ethylhexylmonocarbonate, t-hexyl peroxybenzoate, t-butylperoxyacetate and the like.

As the dialkyl peroxides, α,α′-bis(t-butylperoxy)diisopropylbenzene,dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butylcumylperoxide and the like may be used.

As the hydroperoxides, diisopropylbenzene hydroperoxide, cumenehydroperoxide and the like may be used.

As the diacyl peroxides, isobutyl peroxide, 2,4-dichlorobenzoylperoxide, 3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, lauroylperoxide, stearoyl peroxide, succinic peroxide, benzoyl peroxytoluene,benzoyl peroxide and the like may be used.

As the peroxydicarbonates, di-n-propyl peroxydicarbonate, diisopropylperoxydicarbonate, bis(4-t-butylcyclohexyl)peroxydicarbonate,di(2-ethoxyethyl)peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate,di(3-methoxybutyl)peroxydicarbonate,di(3-methyl-3-methoxybutyl)peroxydicarbonate and the like may be used.

As the peroxyketals, 1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t-hexylperoxy)cyclohexane,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t-butylperoxy)cyclododecane, 2,2-bis(t-butylperoxy)decane andthe like may be used.

As the silyl peroxides, t-butyltrimethylsilyl peroxide,bis(t-butyl)dimethylsilyl peroxide, t-butyltrivinylsilyl peroxide,bis(t-butyl)divinylsilyl peroxide, tris(t-butyl)vinylsilyl peroxide,t-butyltriallylsilyl peroxide, bis(t-butyl)diallylsilyl peroxide,tris(t-butyl)allylsilyl peroxide and the like may be used.

Any of these curing agents capable of generating free radicals may beused alone or in combination, and a decomposition accelerator orinhibitor may be used in combination.

These curing agents may also be coated with a polymeric substance ofpolyurethane type or polyester type so as to be made into microcapsules.Such curing agents are preferred because their pot life can be madelonger.

The radical-polymerizable substance used in the present invention is asubstance having a functional group capable of undergoing radicalpolymerization, and may include acrylates, methacrylates, maleimidecompounds and the like. The radical-polymerizable substance may be usedin the state of either of a monomer and an oligomer. Such monomer andoligomer may also be used in combination.

As specific examples of the acrylates (methacrylates inclusive), theyinclude methyl acrylate, ethyl acrylate, isopropyl acrylate, isobutylacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate,trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate,2-hydroxy-1,3-diacryloxypropane,2,2-bis[4-(acryloxymethoxy)phenyl]propane,2,2-bis[4-(acryloxypolyethoxy)phenyl]propane, dicyclopentenyl acrylate,tricyclodecanyl acrylate, tris(acryloyloxyethyl)isocyanurate and thelike. Any of these may be used alone or in combination. If necessary, apolymerization inhibitor such as hydroquinones and methyl etherhydroquinones may appropriately be used. Also, an instance where theradical-polymerizable substance has a dicyclopentenyl group and/or atricyclodecanyl group and/or a triazine ring is preferred because heatresistance is improved.

The maleimide compounds may include those having at least two maleimidegroups in the molecule, as exemplified by 1-methyl-2,4-bismaleimidebenzene, N,N′-m-phenylenebismaleimide, N,N′-p-phenylenebismaleimide,N,N′-m-toluoylenebismaleimide, N,N′-4,4-biphenylenebismaleimide,N,N′-4,4-(3,3′-dimethyl-biphenylene)bismaleimide,N,N′-4,4-(3,3′-dimethyldiphenylmethane)bismaleimide,N,N′-4,4-(3,3′-diethyldiphenylmethane)bismaleimide,N,N′-4,4-diphenylmethanebismaleimide,N,N′-4,4-diphenylpropanebismaleimide, N,N′-4,4-diphenyl etherbismaleimide, N,N′-3,3′-diphenyl sulfone bismaleimide.2,2-bis[4-(4-maleimidophenoxy)phenyl]propane,2,2-bis[3-s-butyl-4-(4-maleimidophenoxy)phenyl]propane,1,1-bis[4-(4-maleimidophenoxy)phenyl]decane,4,4′-cyclohexylidene-bis[1-(4-maleimidophenoxy)-2-cyclo hexylbenzene and2,2-bis[4-(4-maleimidophenoxy)phenyl]hexafluoropropane.

Any of these may be used alone or in combination.

Use of the above radical-polymerizable substance in combination with aradical-polymerizable substance having the phosphate structurerepresented by the above chemical formula (a) brings about animprovement in bonding strength on the surface of an inorganic mattersuch as metal. The radical-polymerizable substance may preferably bemixed in an amount of from 0.1 to 10 parts by weight, and morepreferably from 0.5 to 5 parts by weight, based on 100 parts by weightof the total weight of the hydroxyl-group-containing resin having amolecular weight of 10,000 or more and radical-polymerizable substance.

The radical-polymerizable substance having the phosphate structure canbe obtained as a reaction product of phosphoric anhydride with2-hydroxyethyl acrylate or methacrylate. Stated specifically, it mayinclude mono(2-methacryloyloxyethyl)acid phosphate anddi(2-methacryloyloxyethyl)acid phosphate or the like. Any of these maybe used alone or in combination.

As the hydroxyl-group-containing resin having a molecular weight of10,000 or more, polymers such as polyvinyl butyral, polyvinyl formal,polyamide, polyester, phenol resin, epoxy resin and phenoxy resin may beused, which exhibit superior stress relaxation properties at the time ofcuring and bring about an improvement in adhesion attributable tohydroxyl groups. Those obtained by modifying any of these polymers withradical-polymerizable functional groups are more preferred because heatresistance is improved. In such an instance, they arehydroxyl-group-containing resins having a molecular weight of 10,000 ormore and also radical-polymerizable substances.

These polymers may preferably have a molecular weight of 10,000 or more,but those having a molecular weight of 1,000,000 or more tend to havepoor mixing properties.

As the hydroxyl-group-containing resin having a molecular weight of10,000 or more, a hydroxyl-group-containing resin having a Tg (glasstransition temperature) of 40° C. or above and having a molecular weightof 10,000 or more may be used, and phenoxy resin may be used. Thehydroxyl-group-containing resin having a molecular weight of 10,000 ormore may be modified with a carboxyl-group-containing elastomer, anepoxy-group-containing elastomer or a radical-polymerizable functionalgroup. Those modified with the radical-polymerizable functional groupare preferred because heat resistance is improved.

The phenoxy resin is a resin obtained by allowing a bifunctional phenolto react with an epihalohydrin to have a high molecular weight, orsubjecting a bifunctional epoxy resin and a bifunctional phenol topolyaddition reaction. Stated specifically, it can be obtained byallowing 1 mole of a bifunctional phenol to react with 0.985 to 1.015mole of an epihalohydrin in the presence of an alkali metal hydroxide,in a non-reactive solvent and at a temperature of from 40 to 120° C.

In view of mechanical properties and thermal properties of the resin,particularly preferred is a resin obtained using a bifunctional epoxyresin and a bifunctional phenol which are mixed in an equivalent weightratio of epoxy group/phenolic hydroxyl group=1/0.9 to 1/1.1, and bysubjecting them to polyaddition reaction in the presence of a catalystsuch as an alkali metal compound, an organic phosphorus compound or acyclic amine compound, in an organic solvent having a boiling point of120° C. or above of such as amides, ethers, ketones, lactones oralcohols, and at a reaction solid matter concentration of 50% by weightor less while heating the system to 50 to 200° C.

The bifunctional epoxy resin may include bisphenol-A epoxy resin,bisphenol-F epoxy resin, bisphenol-AD epoxy resin, bisphenol-S epoxyresin, and alkylene oxide addition products, halides (such astetrabromophenol epoxy resin) or hydrogenation products of these, aswell as alicyclic epoxy resins, aliphatic chain epoxy resins and halidesor hydrogenation products of these.

These compounds may have any molecular weight. Especially when reactedwith the bifunctional phenol, those having a purity as high as possibleare preferred. These compounds may be used in combination of some kinds.

The epihalohydrin may include epichlorohydrin, epibromohydrin andepiiodohydrin.

The bifunctional phenol may be any phenols so long as they are compoundshaving two phenolic hydroxyl groups, as exemplified by monocyclicbifunctional phenols such as hydroquinone, 2-bromohydroquinone,resorcinol and catechol, bisphenols such as bisphenol A, bisphenol F,bisphenol AD and bisphenol S, dihydroxybiphenyls such as4,4′-dihydroxybiphenyl, dihydroxyphenyl ethers such asbis(4-hydroxyphenyl)ether, and any of these compounds into the aromaticring of the phenolic skeleton of which a straight-chain alkyl group, abranched alkyl group, an aryl group, a methylol group, an allyl group, acyclic aliphatic group, a halogen atom (to form, e.g.,tetrabromobisphenol A), a nitro group or the like has been introduced,and also polycyclic bifunctional phenols formed by introducing astraight-chain alkyl group, a branched alkyl group, an allyl group, anally group with a substituent, a cyclic aliphatic group or analkoxycarbonyl group into the carbon atom present at the center of thebisphenolic skeleton of any of these compounds.

Stated specifically, the bifunctional phenol may include4,4′-(1-methylethylidene)bis[2-methylphenol],4,4′-methylenebis[2-methylphenol],4,4′-(1-methylethylidene)bis[2-(1-methylethyl)phenol],4,4′-(1-methylethylidene)bis[2-(1,1-methylpropyl)phenol],4,4′-(1-methylethylidene)bis[2-(1,1-dimethylethyl)phenol],tetramethylbisphenol A, tetramethylbisphenol F,4,4′-methylenebis[2,6-bis(1,1-dimethylethyl)phenol],4,4′-(1-methylethylidene)bis[2,6-di(1,1-dimethylethyl)phenol],4,4′-(1-methylethylidene)bis[2-(2-propenyl)phenol],4,4′-methylenebis[2-(2-propenyl(phenol),4,4′-(1-methylethylidene)bis[2-(1-phenylethyl)phenol],3,3′-dimethyl[1,1′-biphenyl]-4,4′-diol,3,3′,5,5′-tetramethyl[1,1′-biphenyl]-4,4′-diol,3,3′,5,5′-tetra-t-butyl[1,1′-biphenyl]-4,4′-diol,3,3′-bis(2-propenyl)-[1,1′-biphenyl]-4,4′-diol,4,4′-(1-methylethylidene)bis[2-methyl-6-hydroxymethylphenol],tetramethylolbisphenol A,3,3′,5,5′-tetrakis(hydroxymethyl)-(1,1′-biphenyl)-4,4′diol,4,4′-(1-methylethylidene)bis[2-phenylphenol],4,4′-(1-methylethylidene)bis[2-cyclohexylphenol],4,4′-methylenebis(2-cyclohexyl-5-methylphenol],4,4′-(1-methylpropylidene)bisphenol,4,4′-(1-methylheptylidene)bisphenol, 4,4′-(1-methyloctylidene)bisphenol,4,4′-(1,3-dimethylbutylidene)bisphenol,4,4′-(2-ethylhexylidene)bisphenol, 4,4′-(2-methylpropylidene)bisphenol,4,4′-propylidenebisphenol, 4,4′-(1-ethylpropylidene)bisphenol,4,4′-(3-methylbutylidene)bisphenol, 4,4′-(1-phenylethylidene)bisphenol,4,4′-(phenylmethylene)bisphenol, 4,4′-(diphenylmethylene)bisphenol,4,4′-[1-(4-nitrophenyl)ethylidene]bisphenol,4,4′-[1-(4-aminophenyl)ethylidene]bisphenol,4,4′-(4-bromophenyl)methylenebisphenol,4,4′-(4-chlorophenyl)methylenebisphenol,4,4′-(4-fluorophenyl)methylenebisphenol,4,4′-(2-methylpropylidene)bis[3-methyl-6-(1,1-dimethylethyl)phenol],4,4′-(1-ethylpropylidene)bis[2-methylphenol],4,4′-(1-phenylethylidene)bis[2-methylphenol],4,4′-(phenylmethylene)bis(2,3,5-trimethylphenol),4,4′-(phenylethylidene)bis[2-(1,1-dimethylethyl)phenol],4,4′-(1-methylpropylidene)bis[2-cyclohexyl-5-methylphenol],4,4′-(1-phenylethylidene)bis[2-phenylphenol],4,4′-butylidenebis[3-methyl-6-(1,1-dimethylethyl)phenol],4-hydroxy-α-(4-hydroxyphenyl)-α-methylbenzene acetic acid methyl ester,4-hydroxy-α-(4-hydroxyphenyl)-α-methylbenzene acetic acid ethyl ester,4-hydroxy-α-(4-hydroxyphenyl)benzene acetic acid butyl ester,tetrabromobisphenol A, tetrabromobisphenol F, tetrabromobisphenol AD,4,4′-(1-methylethylene)bis[2,6-dichlorophenol],4,4′-(1-methylethylidene)bis[2-chlorophenol],4,4′-(1-methylethylidene)bis[2-chloro-6-methylphenol],4,4′-methylenebis[2-fluorophenol],4,4′-methylenebis[2,6-difluorophenol],4,4′-isopropylidenebis[2-fluorophenol],3,3′-difluoro-[1,1′-diphenyl]-4,4′-diol,3,3′,5,5′-tetrafluoro-[1,1′-biphenyl]-4,4′-diol,4,4′-(phenylmethylene)bis[2-fluorophenol],4,4′-(4-fluorophenyl)methylenebis[2-fluorophenol],4,4′-(phenylmethylene)bis[2,6-difluorophenol],4,4′-(4-fluorophenyl)methylenebis[2,6-difluorophenol],4,4′-(diphenylmethylene)bis[2-fluorophenol],4,4′-(diphenylmethylene)bis[2,6-difluorophenol],4,4′-(1-methylethylene)bis[2-nitrophenol] and the like.

The polycyclic bifunctional phenols other than these may include1,4-naphthalene diol, 1,5-naphthalene diol, 1,6-naphthalene diol,1,7-naphthalene diol, 2,7-naphthalene diol, 4,4′-dihydroxydiphenylether, bis(4-hydroxyphenyl)methanone, 4,4′-cyclohexylidenebisphenol,4,4′-cyclohexylidenebis[2-methylphenol], 4,4′-cyclopentylidenebisphenol,4,4′-cyclopentylidenebis[2-methylphenol],4,4′-cyclohexylidenebis[2,6-dimethylphenol],4,4′-cyclohexylidenebis[2-(1,1-dimethylethyl)phenol],4,4′-cyclohexylidenebis[2-cyclohexylphenol],4,4′-(1,2-ethanediyl)bisphenol, 4,4′-cyclohexylidenebis[2-phenylphenol],4,4′-[1,4-phenylenebis(1-methylethylidene)]bis[2-methyl phenol],4,4′-[1,3-phenylenebis(1-methylethylidene)]bisphenol,4,4′-[1,4-phenylenebis(1-methylethylidene)]bisphenol,4,4′-[1,4-phenylenebis(1-methylethylidene)]bis[2-methyl-6-hydroxymethylphenol],4-{1-[4-(4-hydroxy-3-methylphenyl)-4-methylcyclohexyl]-1-methylethyl}-2-methylphenol,4-{1-[4-(4-hydroxy-3,5-dimethylphenyl)-4-methylcyclohexyl]-1-methylethyl}-2,6-dimethylphenol,4,4′-(1,2-ethanediyl)bis[2,6-di-(1,1-dimethylethyl)phenol],4,4′-(dimethylsilylene)bisphenol,1,3-bis(p-hydroxyphenyl)-1,1,3,3-tetramethyldisiloxane, siliconeoligomers both-end terminated with p-hydroxyphenyl groups, and2,2′-methylidenebisphenol, 2,2′-methylethylidenebisphenol,2,2′-ethylidenebisphenol or the like into the aromatic ring of thephenolic skeleton of which a straight-chain alkyl group, a branchedalkyl group, an aryl group, a methylol group or an allyl group has beenintroduced.

Stated specifically, the last-mentioned ones may include2,2′-methylidenebis[4-methylphenol], 2,2′-ethylidenebis[4-methylphenol],2,2′-methylidenebis[4,6-dimethylphenol],2,2′-(1-methylethylidene)bis[4,6-dimethylphenol],2,2′-(1-methylethylidene)bis[4-sec-butylphenol],2,2′-methylidenebis[6-(1,1-dimethylethyl)-4-methylphenol],2,2′-ethylidenebis[4,6-di(1,1-dimethylethyl)phenol],2,2′-methylidenebis[4-nonylphenol],2,2′-methylidenebis[3-methyl-4,6-di(1,1-dimethylethyl)phenol],2,2′-(2-methylpropylidene)]bis[2,4-dimethylphenol],2,2′-ethylidenebis[4-(1,1-dimethylethyl)phenol],2,2′-methylidenebis[2,4-di(t-butyl)-5-methylphenol),2,2′-methylidenebis(4-phenylphenol),2,2′-methylidenebis(4-methyl-6-hydroxymethylphenol),2,2′-methylenebis[6-(2-propenyl)phenol] and the like.

These compounds may be used in combination of some kinds.

Solution formed after the reaction is completed may be purified byreprecipitation using a bad solvent such as methanol to obtain theproduct as a solid phenoxy resin. The phenoxy resin thus produced may beused in combination of two or more.

To achieve the object of the present invention, the phenoxy resin maypreferably be a resin comprised of a first constituent unit representedby the following Formula (I) and/or a second constituent unitrepresented by the following Formula (II) and containing at least onefirst constituent unit in the molecule. In a case where a copolymerhaving both the first constituent unit and the second constituent unitis used as the phenoxy resin, the phenoxy resin may preferably containat least 10 mole % of the first constituent unit, and may morepreferably in a copolymerization ratio of first constituent unit:secondconstituent unit=2:8 to 8:2. In a case where two or more types ofphenoxy resins are used, at least one of them may preferably becomprised of the first constituent unit and/or the second constituentunit and contain at least one first constituent unit in the molecule.

In the formulae, R¹ to R⁴ are each independently selected from ahydrogen atom, an alkyl group having 1 to 4 carbon atoms (such as amethyl group, an ethyl group, a propyl group, a butyl group, anisopropyl group or an isobutyl group) and an electron-withdrawing group.At least one of R¹ to R⁴ is an electron-withdrawing group. Theelectron-withdrawing group refers to a group whose Hammett's substituentconstant σ has the positive value (“Chemical Dictionary”, pp. 833-834,1986, Morikita Publish. Inc.). It may include, e.g., halogens such as afluorine atom, a chlorine atom and a bromine atom, a trifluoromethylgroup, a trichloromethyl group, a tribromomethyl group, a nitro group, anitrile group, alkoxyl groups such as a methoxyl group and an ethoxylgroup, a carboxyl group, alkylcarbonyl groups such as a methylcarbonylgroup and an ethylcarbonyl group, alkoxycarbonyl groups such as amethoxycarbonyl group and an ethoxycarbonyl group, and alkylsulfonylgroups. The halogens are preferred.

R⁵ to R⁸ are each independently selected from a hydrogen atom and analkyl group having 1 to 4 carbon atoms (such as a methyl group, an ethylgroup, a propyl group, a butyl group, an isopropyl group or an isobutylgroup).

X¹ and X² each represent a divalent organic group or linkage. There areno particular limitations on the divalent organic group represented byX¹ and X². For example, it may include the following.

The phenoxy resin as described above can be obtained by using synthesismaterials at least one of which is the bifunctional epoxy resin and/orbifunctional phenol which have a hydrogen atom, an alkyl group having 1to 4 carbon atoms or an electron-withdrawing group.

As specific examples of such an phenoxy resin, it may include, e.g., arandom copolymer comprised of a repeating unit represented by thefollowing structural formula (III) and a repeating unit represented bythe following structural formula (IV):

a polymer comprised of a repeating unit represented by the followingstructural formula (V):

a polymer comprised of a repeating unit represented by the followingstructural formula (VI):

a polymer comprised of a repeating unit represented by the followingstructural formula (VII):

and the like.

In order for cured products to exhibit excellent properties such asflexibility, toughness and film-forming properties, a phenoxy resin isused which preferably has an average molecular weight (weight-averagemolecular weight in terms of polystyrene as measured by gel permeationchromatography) of at least 10,000, more preferably at least 20,000, andstill more preferably at least 30,000. As commercially availableproducts, it may include, e.g., PKHH and PAHJ (available from UnionCarbide Corporation), YPB-43C, YPB-43D, YPB-43G, YPB-43m and YP-50 orYPB-40ASB25 and YPB-40AM40 (available from Tohto Kasei Co., Ltd.), whichmay be purified by reprecipitation.

The carboxyl-group-containing elastomer and the epoxy-group-containingelastomer may be any elastomers so long as they are those having acarboxyl group or epoxy group at the molecular terminal or in themolecular chain, including, e.g., butadiene copolymers, acryliccopolymers, polyether-urethane rubbers, polyester-urethane rubbers,polyamide-urethane rubbers and silicone rubbers. Butadiene type polymersare preferred. Incidentally, the butadiene type polymers may includebutadiene polymer, butadiene-styrene copolymer, butadiene-acrylonitrilecopolymer and the like. In particular, butadiene-acrylonitrile copolymeris preferred.

The carboxyl-group-containing elastomer may preferably have aweight-average molecular weight ranging from 500 to 1,000,000, morepreferably from 1,000 to 800,000, and still more preferably from 1,000to 10,000.

The quantity of a component compatible with the phenoxy resin containedin the elastomer skeleton may preferably be so determined that thephenoxy phase and the elastomer phase may be kept phase-separated,because the both may dissolve mutually if such a component is in a largequantity. The quantity of this component can be regulated as desired inaccordance with the structure (SP value) of phenoxy resins and the heatresistance and mechanical strength of resins having been modified. Forexample, in the case of the butadiene-acrylonitrile copolymer, thecontent of the acrylonitrile may preferably be set to be not more than40% by weight, more preferably from 5 to 40% by weight, and still morepreferably from 10 to 30% by weight. As commercially available products,it may include, e.g., HYCAR CTBN1300x31, HYCAR CTBN1300x8, HYCARCTBN1300x13, HYCAR CTBNX1300x9, HYCAR CTBNX1009-SP and HYCAR CTB200x162(available from Ube Industries, Ltd.), NIPOL DN 601 (available fromNippon Zeon Co., Ltd.), Nisso PB C-1000, C-2000 (available from NipponSoda Co., Ltd.), and ELC-4 (available from Japan Synthetic Rubber Co.,Ltd.).

When the circuit connecting material of the present invention is usedfor electronic parts and devices such as semiconductors, ionicimpurities in the material may preferably be made as less as possible.Accordingly, in these carboxyl-group-containing elastomers, too, alkalimetal ions such as Na⁺ and K⁺ in the polymer may preferably be not morethan 10 ppm, and more preferably not more than 5 ppm, and Cl⁻ maypreferably be not more than 400 ppm, more preferably not more than 100ppm, and still more preferably not more than 40 ppm.

Such a phase-separated structural product of the present invention canbe produced, e.g., in the following way.

First, the phenoxy resin is dissolved in a solvent, and thecarboxyl-group-containing elastomer is dissolved in the resultantsolution (the volume ratio of the phenoxy resin and the elastomer may beset as desired in accordance with the target values of flexibility,toughness and bonding strength of cured products, required in purposesfor which the products are used, where the ratio of phenoxy resin:elastomer may preferably be in the range of from 60:40 to 90:10, andmore preferably from 66:33 to 87:13).

The solvent used when produced may be any solvents so long as they arethose capable of dissolving the phenoxy resin andcarboxyl-group-containing elastomer. In an instance where a blockedisocyanate, described later, is added to the solution formed afterheat-mixing, the solvent must be a solvent inert to isocyanate groups.

Next, the interior of the solution is well displaced with nitrogen, andthereafter the solution is mixed with stirring while heating it at about100° C. to about 220° C., and preferably about 130° C. to about 180° C.,in an atmosphere of nitrogen until the solution becomes semitransparentor transparent at normal temperature and preferably it comes to have aconstant value of viscosity. The heat-mixing may preferably be carriedout while refluxing the solvent.

The elastomer-modified phenoxy resin solution thus formed after theheat-mixing is completed may be purified by reprecipitation using a badsolvent such as methanol to obtain the product as a solidphase-separated structural product. The mechanism of such modificationis unclear, but it has been ascertained that, in ¹H-NMR spectra beforeand after modification, the integral value corresponding to protons ofthe methine bonded to the hydroxyl group in the phenoxy resin skeletonhas decreased after modification. It has also been ascertained that, inFT-IR (Fourier-transform infrared absorption) spectra, remarkablechanges have occurred in the spectra in the regions of from 3,460 cm⁻¹to 3,560 cm⁻¹ and from 1,610 cm⁻¹ to 1,640 cm⁻¹ which are not seen inproducts obtained by merely blending elastomers. From these facts, it ispresumed that at least part of carboxyl groups of thecarboxyl-group-containing elastomer and at least part of hydroxyl groupsof the phenoxy resin form an ester linkage.

In the elastomer-modified phenoxy resin which is obtained in this way,the phenoxy resin and the carboxyl-group-containing elastomer make upphase separation, and this phase-separated structural product alone canform an optically transparent or semitransparent film-like product. Sucha film-like product, when formed in a layer thickness of 75 μm, maypreferably have a light transmittance at 500 nm wavelength, of 10% ormore with respect to the light transmittance of air. The lighttransmittance may more preferably be from 20 to 90%, and still morepreferably from 30 to 85%.

Whether or not the phase separation has been made up can be ascertainedby observation with a scanning or transmission electron microscope or anatomic force microscope or by dynamic viscoelasticity measurement, lightscattering or small-angle X-ray scattering (“Polymer Blends”, pp.80-124, CMC Co. Ltd.). For example, in the dynamic viscoelasticitymeasurement, it may be ascertained by the phenomenon that the tan δ(loss elastic modulus G″/storage elastic modulus G′) peak of principaldispersion of the elastomer phase and the tan δ peak of principaldispersion of the phenoxy resin phase are present independently.

The phase-separated structural product of the present invention maypreferably have a microscopic phase-separated structure wherein, in ascanning electron microscope of the film-like product, the elastomerphase and the phenoxy resin phase are dispersed in the form of verysmall particles of submicroscopic order of about 0.1 to 0.3 μm. Such afilm-like product of phase-separated structure stands opticallytransparent or semitransparent. More specifically, the lighttransmittance of the phase-separated structural product of the presentinvention, when formed in the film-like product with a layer thicknessof 75 μm, is 10% or more with respect to the light transmittance of air.

The phase-separated structure of the elastomer-modified phenoxy resinobtained in the present invention may include, e.g., the microscopicphase-separated structure formed of the elastomer phase and phenoxyresin phase, and a microscopic phase-separated structure formed ofmicroscopic domains connected with one another, which are structureshitherto unknown in the mixing of carboxyl-group-containing elastomerswith phenoxy resins. Such a microscopic phase-separated structure isconsidered to be one factor that brings about an improvement in bondingstrength to adherends.

The hydroxyl-group-containing resin having a molecular weight of 10,000or more and the radical-polymerizable substance may preferably beformulated in such amounts of (hydroxyl-group-containing resin having amolecular weight of 10,000 or more/radical-polymerizable substance) offrom 10/90 to 90/10, and more preferably from 30/70 to 70/30, in weightratio.

In the circuit-connecting material of the present invention, a copolymeracrylic rubber which is a polymer or copolymer having as a monomercomponent at least one of acrylic acid, acrylate, methacrylate andacrylonitrile and contains glycidyl acrylate or glycidyl methacrylatecontaining a glycidyl ether group may also be used in combination. Sucha material brings about superior stress relaxation, and is preferred.The acrylic rubber may preferably have a molecular weight (weightaverage) of 200,000 or more in view of an improvement of cohesive forceof adhesives.

The circuit-connecting material may also contain a filler, a softener,an accelerator, an anti-aging agent, a colorant, a flame retardant, athixotropic agent, a coupling agent and a phenol resin, as well as amelamine resin, a kind of isocyanates and the like.

The material containing a filler can improve connection reliability andso forth, and is preferred. The filler may be used so long as itsmaximum particle diameter is smaller than the particle diameter of theconductive particles, and may preferably be added in an amount rangingfrom 5 to 60 parts by volume based on 100 parts by volume of theadhesive resin component. Its addition in an amount more than 60 partsby volume may saturate the effect of improving reliability, and, in anamount less than 5 part by volume, may bring about less effect ofaddition.

As the coupling agent, those containing a vinyl group, an acrylic group,an amino group, an epoxy group or an isocyanate group are preferred inview of an improvement of adhesion.

The circuit-connecting material of the present invention is a connectingmaterial which is interposed between circuit electrodes facing eachother and electrically connects the electrodes in the pressing directionby pressing the facing electrodes against each other, wherein it has, inmeasurement with a differential scanning calorimeter (DSC) at 10°C./min., an exothermic reaction arising temperature (Ta) within a rangeof from 70° C. to 110° C., a peak temperature (Tp) of Ta+5 to 30° C. andan end temperature (Te) of 160° C. or below.

Conventional epoxy resin film-like adhesives, though having an excellentoperability, have been required to be heated at about 140 to 180° C.when connected in a time of about 20 seconds, and at about 180 to 210°C. when connected in 10 seconds. This is because catalyst type curingagents, which are inert at normal temperature, are used so that bothshort-time curability (rapid curability) and storage stability(storability) can be achieved to attain a better stability, and hence nosufficient reaction can take place when cured. In recent years, in thefield of precision electronic equipment, circuits are being made higherin density, resulting in very small width of electrodes and very narrowspaces between electrodes. Hence, there has been a problem that thewiring comes off, separates or positionally deviates under connectingconditions for circuit-connecting materials making use of conventionalepoxy resin adhesives. Also, in order to improve production efficiency,it is increasingly sought to shorten the connecting time to 10 secondsor less, making it indispensable to attain low-temperature rapidcurability.

The circuit-connecting material of the present invention can provide anelectric and electronic circuit-connecting material which can cure uponheating at 140 to 180° C. for about 10 seconds to connect circuitelectrodes, and also has a relatively long pot life at room temperature.

The circuit-connecting material of the present invention, even when itdoes not contain any conductive particles, can achieve connection bybringing the facing circuit electrodes into direct contact whenconnected, but stabler connection can be achieved in a case where itcontains conductive particles.

The conductive particles may include particles of metals such as Au, Ag,Ni, Cu and solder or carbon. In order to attain a sufficient pot life,they may preferably have surface layers formed of not a transition metalsuch as Ni or Cu but a noble metal such as Au, Ag or a platinum groupmetal, and more preferably be formed of Au. Particles comprising atransition metal such as Ni and surface-coated with a noble metal suchas Au may also be used. In a case of particles comprisingnon-conductive, glass or ceramic or plastic and on which the aboveconductive layers have been formed by coating to provide outermostlayers of a noble metal and cores of plastic etc., or in a case ofheat-fusion metal particles, the particles are deformable upon heatingand pressing and hence can have a larger area of contact with electrodesat the time of connection, bringing about an improvement in reliability.Thus, such particles are preferred. Such coat layers of a noble metalmay preferably be in a thickness of 100 Å or larger in order to attain agood resistance. However, in a case where layers of a noble metal areprovided on particles of a transition metal such as Ni, it maypreferably be in a thickness of 300 Å or larger, since free radicalsgenerated by the redox action caused when, e.g., the noble-metal layerscome off during the mixing and dispersion of conductive particles maycause a lowering of storage stability. The conductive particles are usedproperly in accordance with purposes, within the range of from 0.1 to 30parts by volume based on 100 parts by volume of the adhesive resincomponent. In order to prevent adjoining circuits from short-circuitingbecause of any excess conductive particles, the conductive particles maymore preferably be used within the range of from 0.1 to 10 parts byvolume.

The circuit-connecting material may also be separated into two or morelayers, and separated into a layer containing the curing agent capableof generating free radicals upon heating and a layer containing theconductive particles. In such an instance, it can be improved in potlife.

The circuit-connecting material of the present invention may also beused as a film-like adhesive for bonding IC chips to a chip-mountingsubstrate or for bonding electric circuits mutually.

The circuit-connecting material of the present invention may still alsobe used when semiconductor chips are bonded and fastened to a substratewith an adhesive film by face-down bonding and at the same timeelectrodes of the both are electrically connected to one another.

More specifically, a first circuit member having first connectingterminals and a second circuit member having second connecting terminalsmay be disposed in such a way that the first connecting terminals andthe second connecting terminals face each other, and thecircuit-connecting material (film-like adhesive) of the presentinvention may be interposed between the first connecting terminals andthe second connecting terminals which face each other, followed byheating and pressing to electrically connect the first connectingterminals and the second connecting terminals which face each other.

As such circuit members, chip component parts such as semiconductorchips, resistor chips and capacitor chips and substrates such asprinted-wiring substrates are used.

Usually, in these circuit members, a large number of connectingterminals (which may be in a singular number as occasion calls) areprovided. At least one set of the circuit members are disposed in such away that at least part of the connecting terminals provided on thesecircuit members face each other, and the adhesive is interposed betweenthe connecting terminals facing each other, followed by heating andpressing to electrically connect the connecting terminals facing eachother.

At least one set of the circuit members is heated and pressed, wherebythe connecting terminals facing each other can electrically be connectedin direct contact or via conductive particles of an anisotropicconductive adhesive.

In the circuit-connecting material of the present invention, theadhesive melt-flows at the time of connection and, after the circuitelectrodes facing each other have been connected, cures to keep theconnection, thus the fluidity of the adhesive is an important factor.Using glass sheets of 0.7 mm thick and 15 mm×15 mm in size and when acircuit-connecting material of 35 μm thick and 5 mm×5 mm in size is heldbetween the glass sheets and these are heated and pressed at 150° C. and2 MPa for 10 seconds, the value of fluidity (B)/(A) expressed on thebasis of an initial area (A) and an area (B) after heating and pressingmay preferably be from 1.3 to 3.0, and more preferably from 1.5 to 2.5.If the value is less than 1.3, the fluidity may be so poor as to enableno good connection in some cases. If it is more than 3.0, air bubblestend to occur to make reliability poor in some cases.

The circuit-connecting material of the present invention may preferablyhave a modulus of elasticity of from 100 to 2,000 MPa, and morepreferably from 1,000 to 1,800 MPa, at 40° C. after curing.

The circuit terminal connecting method of the present invention ischaracterized in that the circuit-connecting material capable of curingupon radical polymerization is formed on one circuit electrode whosesurface is formed of a metal selected from gold, silver, tin andplatinum group metals, and thereafter the other circuit electrode isregistered, followed by heating and pressing to connect them.

The circuit electrode connected structure of the present invention is acircuit electrode connected structure wherein circuit electrodes facingeach other is electrically connected via a circuit-connecting material,and is characterized in that the surface of at least one of the facingconnecting terminals is formed of a metal selected from gold, silver,tin and platinum group metals and the circuit-connecting material is acircuit-connecting material capable of curing upon radicalpolymerization.

As the circuit-connecting material capable of curing upon radicalpolymerization, an anisotropic conductive adhesive containing conductiveparticles may be used. As the conductive particles of such ananisotropic conductive adhesive, conductive particles are used whosesurfaces are formed of a noble metal selected from gold, silver andplatinum group metals.

As a result of extensive studies on connecting methods of electricallyconnecting circuit electrodes facing each other by the use of adhesivescapable of curing upon radical polymerization, good electricalconnection can be attained when the surface of at least one of thefacing connecting terminals is formed of gold, silver, a platinum groupmetal or tin, and a radical-polymerizable adhesive is laid and formed onthat surface (provisional connection), followed by main connection.

FIG. 1 is a cross-sectional view showing the step of provisionalconnection of circuit substrates, illustrating an embodiment of thepresent invention. FIG. 2 is a cross-sectional view showing the step ofmain connection of circuit substrates, illustrating an embodiment of thepresent invention. In these figures, reference numerals 1 and 2 denotesubstrates; 1-a and 2-a, circuit electrodes; 3, an adhesive; 4,conductive particles; and 5, a hot plate.

The substrate 1 used in the present invention is an insulating substratemade of silicon or gallium arsenic as in semiconductor chips, or glass,ceramic, a glass-epoxy composite or plastic, and the substrate 2 facingthis substrate is also made of the similar material.

The circuit electrodes 1-a are provided on the surface of the substrate1, using copper foil, and gold surface layers are formed thereon. Thesurface layers are formed of gold, silver, a platinum group metal ortin, any of which may be selected and any of which may be used incombination. Also, a plurality of metals may be combined in the mannerof, e.g., copper/nickel/gold to provide multi-layer configuration. Thecircuit electrodes 2-a are provided on the surface of the substrate 2,using copper foil, and tin surface layers are formed thereon.

The substrates provided with the circuit electrodes may preferablypreviously be subjected to heat treatment before the step of connectioncarried out using the circuit-connecting material in order to eliminatethe influence of the volatile component due to heating at the time ofconnection. The heat treatment may preferably be made under conditionsof a temperature of 50° C. or above for 1 hour or longer, and morepreferably a temperature of 100° C. or above for 5 hours or longer.

The adhesive 3 is an adhesive comprised essentially of the curing agentcapable of generating free radicals upon heating and the radical-curablesubstance, or may be the radical-curable anisotropic conductive adhesivehaving conductive particles dispersed therein in a prescribed quantity.In the latter, the conductive particles may preferably have surfacesformed of a noble metal selected from gold, silver or a platinum groupmetal. The adhesive 3 is laid and formed (provisional connection) on thesubstrate 1.

As shown in FIG. 2, after the provisional connection, the circuitelectrodes 1-a of the substrate 1 and the circuit electrodes 2-a of thesubstrate 2 are registered, and heat and pressure are applied from theupper part of the substrate 2 by means of the hot plate 5 for aprescribed time to complete the main connection.

When circuit electrodes are connected using a radical-curable adhesivehaving a good reactivity and using circuit electrodes whose surfaces areformed of transition metal such as nickel or copper, radicalpolymerization inevitably proceeds because of redox action after theradical-curable adhesive is laid and formed (provisional connection) onthe circuit electrodes and thereafter left for a certain period of time,so that the adhesive may flow with difficulty to enable no sufficientelectrical connection at the time of main connection. However, thepresent invention enables electric and electronic circuit connectionpromising a low-temperature curability superior to, and a longer potlife than, those of conventional epoxy resin types.

At least one of the substrates provided with the circuit electrodes maybe subjected to heat treatment at a temperature of 50° C. or above for 1hour or longer.

EXAMPLE 1

50 g of phenoxy resin (available from Union Carbide Corp.; trade name:PKHC; average molecular weight: 45,000) was dissolved in a 50/50 (weightratio) mixed solvent of toluene (boiling point: 110.6° C.; SP value:8.90) and ethyl acetate (boiling point: 77.1° C.; SP value: 9.10) toform a solution with a solid content of 40%.

As the radical-polymerizable substance, trihydroxyethyl glycoldimethacrylate (available from Kyoeisha Chemical Co., Ltd.; trade name:80MFA) was used.

As the free-radical-generating agent, a 50% by weight DOP solution oft-hexylperoxy-2-ethyl hexanoate (available from Nippon Oil & Fats Co.,Ltd.; trade name: PERCURE HO) was used.

On the surfaces of polystyrene-core particles, nickel layers of 0.2 μmthick were provided. On the outsides of the nickel layers formed, goldlayers of 0.04 μm thick were provided. Thus, conductive particles of 10μm in average particle diameter were produced.

The phenoxy resin, the trihydroxyethyl glycol dimethacrylate resin andthe t-hexyl peroxy-2-ethylhexanoate were formulated in amounts of 50 g,50 g and 5 g, respectively, in solid weight ratio, and the conductiveparticles were further mixed and dispersed in an amount of 3 parts byvolume based on 100 parts by volume of the resin component. Theresultant dispersion was coated on a one-side surface-treated PET filmof 80 μm thick by means of a coater, followed by hot-air drying at 70°C. for 10 minutes to obtain a circuit-connecting material having anadhesive layer of 35 μm thick.

Using the above circuit-connecting material, flexible printed circuitboards (FPCs) each having 500 lines of copper circuits of 50 μm in linewidth, 100 μm pitch and 18 μm thick were connected to each other over awidth of 2 mm while heating and pressing them at 160° C. and 3 MPa for10 seconds. Here, the circuits were connected by putting the adhesivesurface of the circuit-connecting material on the one FPC, followed byheating and pressing at 70° C. and 5 MPa for 5 seconds to makeprovisional connection, and thereafter peeling the PET film andconnecting the one FPC to the other FPC.

EXAMPLES 2 TO 4

Circuit-connecting materials were obtained in the same manner as inExample 1 except that the trihydroxyethyl glycol dimethacrylate and aphosphate type acrylate (available from Kyoeisha Chemical Co., Ltd.;trade name: P2m) were used as radical-polymerizable substances and thesolid weight ratio of the phenoxy resin/trihydroxyethyl glycoldimethacrylate/phosphate type acrylate was set to be 50 g/49 g/1 g(Example 2), 30 g/69 g/1 g (Example 3) or 70 g/29 g/1 g (Example 4).

Using these circuit-connecting materials, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 5

A circuit-connecting material was obtained in the same manner as inExample 1 except that the amount of the curing agent was changed to 2 g.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 6

A circuit-connecting material was obtained in the same manner as inExample 1 except that the curing agent was changed to t-butylperoxy-2-ethylhexanoate (available from Nippon Oil & Fats Co., Ltd.;trade name: PERBUTYL O).

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 7

100 g of phenoxy resin (PKHC) of 45,000 in average molecular weight wasallowed to react with 25 g of a butadiene-acrylonitrile copolymerterminated with a carboxyl group (HYCAR CTBNX1009-SP, available from UbeIndustries, Ltd.) by a conventional process to produce a phenoxy resinmodified with the butadiene-acrylonitrile copolymer terminated withcarboxyl groups. A circuit-connecting material was obtained in the samemanner as in Example 1 except that this phenoxy resin was used and thesolid weight ratio of the phenoxy resin/trihydroxyethyl glycoldimethacrylate/phosphate type acrylate was set to be 60 g/39 g/1 g.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 8

100 g of phenoxy resin (PKHC) of 45,000 in average molecular weight wasmodified with 25 g of an epoxy-group-containing acrylic copolymer toproduce a modified phenoxy resin. A circuit-connecting material wasobtained in the same manner as in Example 1 except that this phenoxyresin was used and the solid weight ratio of the phenoxyresin/trihydroxyethyl glycol dimethacrylate/phosphate type acrylate wasset to be 60 g/39 g/1 g.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 9

A circuit-connecting material was obtained in the same manner as inExample 1 except that an epoxy-group-containing acrylic copolymer(acrylic rubber) was used and the solid weight ratio of the phenoxyresin/acrylic rubber/trihydroxyethyl glycol dimethacrylate/phosphatetype acrylate was set to be 40 g/20 g/39 g/1 g.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 10

100 g of phenoxy resin (PKHC) of 45,000 in average molecular weight wasallowed to react with 5 g of a monoisocyanate terminated with an acrylicgroup, by a conventional process to produce a phenoxy resin modifiedwith acrylic groups. A circuit-connecting material was obtained in thesame manner as in Example 1 except that this phenoxy resin was used andthe solid weight ratio of the phenoxy resin/trihydroxyethyl glycoldimethacrylate/phosphate type acrylate was set to be 60 g/39 g/1 g.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 11

A circuit-connecting material was obtained in the same manner as inExample 1 except that Ni particles having an average particle diameterof 2 μm and surface-coated with Au (coating thickness: 0.08 μm) wereused as the conductive particles and mixed in an amount of 0.5 parts byvolume.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 12

A circuit-connecting material was obtained in the same manner as inExample 1 except that the conductive particles were replaced with thosehaving particle diameter of 5 μm.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 13

A circuit-connecting material was obtained in the same manner as inExample 1 except that 2,2-bis{4-(acryloxy.diethoxy)phenyl}propane(available from Shin-Nakamura Chemical Co., Ltd.; trade name: A-BPE-4)was used as the radical-polymerizable substance and the solid weightratio of the phenoxyresin/2,2-bis{4-(acryloxy.diethoxy)phenyl}propane/phosphate typeacrylate was set to be 60 g/39 g/1 g.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 14

A circuit-connecting material was obtained in the same manner as inExample 1 except that dicyclopentenyl acrylate (available from KyoeishaChemical Co., Ltd.; trade name: DCP-A) was used as theradical-polymerizable substance and the solid weight ratio of thephenoxy resin/dicyclopentenyl acrylate/phosphate type acrylate was setto be 60 g/39 g/1 g.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 15

A circuit-connecting material was obtained in the same manner as inExample 1 except that tris(acryloyloxyethyl)isocyanurate was used as theradical-polymerizable substance and the solid weight ratio of thephenoxy resin/tris(acryloyloxyethyl)isocyanurate/phosphate type acrylatewas set to be 60 g/39 g/1 g.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 16

A mixture obtained by mixing 30 g of 4,4′-bismaleimide diphenylmethaneand 35 g of diallylbisphenol A with heating at 120° C. for 20 minutesand a phosphate type acrylate (available from Kyoeisha Chemical Co.,Ltd.; trade name: P-2m) were used as radical-polymerizable substances.

Phenoxy resin (PKHC) and nitrile rubber (available from Nippon Zeon Co.,Ltd.; trade name: NIPOL 1072) were used in a ratio of phenoxyresin/nitrile rubber of 20 g/10 g, and were dissolved in 30 g of methylethyl ketone to prepare a solution with a solid content of 50%.

The mixture obtained by mixing 4,4′-bismaleimide diphenylmethane anddiallylbisphenol A with heating at 120° C. for 20 minutes, the phenoxyresin, the nitrile rubber, the phosphate type acrylate and t-hexylperoxy-2-ethylhexanoate were formulated in amounts of 69 g, 20 g, 10 g,1 g and 5 g, respectively, in solid weight ratio, and conductiveparticles were further mixed and dispersed in an amount of 3 parts byvolume. The subsequent procedure of Example 1 was repeated to obtain acircuit-connecting material.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 17

A circuit-connecting material was obtained in the same manner as inExample 14 except that a mixture obtained by mixing 30 g of4,4′-bismaleimide diphenylmethane and 20 g of diallylbisphenol A withheating at 120° C. for 20 minutes was used as the radical-polymerizablesubstance.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

EXAMPLE 18

A circuit-connecting material was obtained in the same manner as inExample 1 except that Ni particles having an average particle diameterof 2 μm and surface-coated with Pd (coating thickness: 0.04 μm) wereused as the conductive particles and mixed in an amount of 0.5% byvolume.

Using this circuit-connecting material, the circuits were connected inthe same manner as in Example 1.

COMPARATIVE EXAMPLE

A circuit-connecting material was obtained in the same manner as inExample 1 except that phenoxy resin (PKHC), bisphenol-A epoxy resin(YL980, trade name of a product of Yuka Shell Epoxy K.K.) and animidazole type microcapsular curing agent (3941HP, trade name of aproduct of Asahi Chemical Industry Co., Ltd.) were used and the solidweight ratio of the phenoxy resin/bisphenol-A epoxy resin/imidazole typemicrocapsular curing agent was set to be 40 g/20 g/40 g.

(Measurement of Connection Resistance)

After the circuits were connected, the values of resistance betweenadjoining circuits of the FPCs having the above connected portion weremeasured at the initial stage and after keeping for 500 hours in ahigh-temperature high-humidity chamber of 85° C. and 85% RH. Theresistance values were indicated as an average (x+3σ) of resistance at150 spots between adjoining circuits. The circuit-connecting materialobtained in Example 1 exhibited a good connection reliability. It wasalso in a low connection resistance at the initial stage and in an onlyslightly higher resistance after the high-temperature high-humiditytest, showing a high durability. The same good reliability as that inExample 1 was also attained in Examples 2 to 18. On the other hand, inComparative Example, the bonding was in a poor state because of aninsufficient curing reaction, resulting in a high connection resistanceat the initial stage.

(Measurement of Adhesive Force)

After the circuits were connected, adhesive force was measured by90-degree peeling at a peel rate of 50 mm/minute. In ComparativeExample, the curing reaction was so insufficient that the adhesive forcewas as low as about 200 gf/cm in bonding strength. In Examples 1 to 18,an adhesive force of as good as about 1,000 gf/cm was attained.

(Evaluation of Storage Stability)

The circuit-connecting materials obtained were treated for 30 days in a30° C. thermostatic chamber, and the circuits were connected in the samemanner as the above to evaluate their storage stability.

In all Examples, the results of connection were obtained which were thesame as those in the state where the circuit-connecting materials werenot treated for 30 days in a 30° C. thermostatic chamber (the initialstage).

(Evaluation of Insulating Properties)

Using the above circuit-connecting materials obtained, a printed-wiringsubstrate having comb circuits with alternately arranged 250 lines ofcopper circuits of 50 μm in line width, 100 μm pitch and 18 μm thick anda flexible printed circuit board (FPC) having 500 lines of coppercircuits of 50 μm in line width, 100 μm pitch and 18 μm thick wereconnected to each other over a width of 2 mm while heating and pressingthem at 160° C. and 3 MPa for 10 seconds. A voltage of 100 V was appliedto the comb circuits of this connected structure to measure the value ofinsulation resistance after a 500-hour, 85° C./85% RH high-temperaturehigh-humidity test.

In all Examples, good insulating properties of 10⁹Ω or above wereattained and any lowering of insulating properties was seen.

(Evaluation of Fluidity)

Using a circuit-connecting material of 35 μm thick and 5 mm×5 mm insize, this was held between glass sheets of 0.7 mm thick and 15 mm×15 mmin size and these were heated and pressed at 150° C. and 2 MPa for 10seconds. The value of fluidity (B)/(A) expressed on the basis of aninitial area (A) and an area (B) after heating and pressing wasdetermined to find that it was 1.9 in Example 1, and also within therange of from 1.3 to 3.0 in Examples 2 to 10.

(Modulus of Elasticity after Curing)

The modulus of elasticity at 40° C. after curing was measured on thecircuit-connecting material of Example 1 to find that it was 1,500 MPa.

(DSC Measurement)

On the circuit-connecting materials obtained, the exothermic reactionarising temperature (Ta), peak temperature (Tp) and end temperature (Te)were determined by means of a differential scanning calorimeter (DSC,manufactured by TA Instrument Co.; trade name: Model 910) in themeasurement at 10° C./min.

In Example 1, the arising temperature (Ta) was 89° C., the peaktemperature (Tp) was 103° C. and the end temperature (Te) was 145° C. InExample 2, the arising temperature (Ta) was 87° C., the peak temperature(Tp) was 99° C. and the end temperature (Te) was 140° C. In Example 7,the arising temperature (Ta) was 92° C., the peak temperature (Tp) was116° C. and the end temperature (Te) was 150° C. In Comparative Example,the arising temperature (Ta) was 86° C., the peak temperature (Tp) was121° C. and the end temperature (Te) was 180° C.

POSSIBILITY OF INDUSTRIAL APPLICATION

As described above, the present invention makes it possible to providean electric and electronic circuit-connecting material having alow-temperature curability superior to, and a longer pot life than,those of conventional epoxy resin types.

1. A circuit-connecting material for interposing between circuitelectrodes facing each other and electrically connecting the electrodes,after curing by heat and pressure, either by direct contact or viaconductive particles present in the material, wherein thecircuit-connecting material comprises: (1) a curing agent capable ofgenerating free radicals upon heating; (2) a hydroxyl-group-containingresin having a weight-average molecular weight of 10,000 or more; (3) afirst radical-polymerizable substance that is not an acidphosphate-containing radical-polymerizable substance; and (4) an acidphosphate-containing radical-polymerizable substance.
 2. Acircuit-connecting material as recited in claim 1, wherein thehydroxyl-group-containing resin having a weight-average molecular weightof 10,000 or more is a phenoxy resin having a weight-average molecularweight of 10,000 or more.
 3. A circuit-connecting material as recited inclaim 2, wherein the acid phosphate-containing radical-polymerizablesubstance is represented by the following chemical formula (I):

wherein n is an integer of 1 to
 3. 4. A circuit-connecting material asrecited in claim 2, wherein the circuit-connecting material has amodulus of elasticity of from 100 to 2000 MPa at 40° C. after curing. 5.A circuit-connecting material as recited in claim 2, wherein thecircuit-connecting material includes two or more layers, wherein a firstlayer contains conductive particles and a second layer contains thecuring agent.
 6. A circuit-connecting material as recited in claim 2,wherein the circuit-connecting material comprises conductive particles.7. A circuit-connecting material as recited in claim 1, wherein thecircuit-connecting material has a modulus of elasticity of from 100 to2000 MPa at 40° C. after curing.
 8. A circuit-connecting material asrecited in claim 1, wherein the circuit-connecting material includes twoor more layers, wherein a first layer contains conductive particles anda second layer contains the curing agent.
 9. A circuit-connectingmaterial as recited in claim 1, wherein the circuit-connecting materialcomprises conductive particles.